Process for manufacturing toluene



enemas 9, 1946 .umrso s'ra'ras mm iorrrca mocass roa MANUFACTURINGTOLUENE 1 David a. Brandt, Westileld, 1s. 1., alsignor to Cities ServiceOil Company, New York, N. Y., a corporation oi Pennsylvania- ApplicationMarch 19, 1942, Serial No. 435,219

1 Glaim. The'present invention relates toan improved process for themanufacture of toluene and more Dflrticularly to the manufacture ofnitration grade toluene from petroleum Many attempts have been made tomanufacture technical benzene. toluene and other aromatic hydrocarbonsfrom petroleum stocks,-b'ut for the most part such processes have notbeen of commercial importance because oi various difficultiesencountered. On the other hand, petroleum stocks, such as gas oil, havebeen successfully converted into products containing substantialpercentages of aromatic hydrocarbons, portions of which are recoveredalong with other constituents boiling within the usual gasoline rangeand used for motor fuel.

It is understood that some attempts have been made to manufacturetoluene from selected petroleum stocks such as those recovered in theextraction of crude oils. or fractions; with such agents as liquidsulphur dioxide. It is also noted in the literature that toluene, alongwith benzene, has been produced in certain processes applied to thecracking of kerosene. For example, Kanep (Chem. Abs. 1935, vol.29. p.5640) pyrolized various kerosene fractions at 700 6., obtaining fromabout 12% to 21% oi aromatic hydrocarbons. He found that the percentageof aromatic hydrocar- 260-368) ent invention comprises in general thesteps of vfirst producing a particularv petroleum stock which may bedirectly converted into a product containing a high percentage oftoluene. This stock is made in accordance with'the features of thepresent invention by starting with a gas oil. kerosene or othersuitablepetroleum distillate, which maybe largely parail'lnic. the stock beingpassed in a confined stream or restrictedcrosssection through a pipestill furnace and cracked therein at a temperature of about 980 F. Thiscracking is preferably completed in the pipe still furnace, but may becompleted to the desired extent by passing the high-temperaturepartially converted products from the furnace into an enlarged reactionchamber where aconsiderable time reaction is allowed for the cracking totake place. At the point where the desired reaction has been completed,the products are immediately and instantly cooled to a temperature be,

low that of further reaction, such, for example.

bons decreased as the boiling range of the kerosene rraction'increased,and that in general the proportion of 1-- he formed was greater thanthat of toluene.

So far as mown, the manufacture oi nitration grade toluene frompetroleum has not been accomplished, at least on a pra'chcai orcommercial.

scale. One of the cultles encountered, in addition to the fact thatrelatively low percentages of toluene were produced, is that ofrecovering nitration grade toluene from the light materlals of similarboiling point which are proggiced alongwith benzene and otherhydrocarns. The primary object of the present invention therefore isrtoovercome the dificulties which have been encountered in previous attptsto.

manufacture toluene from petroleum and at the same time provide acommercial process in which relatively high percentages of toluene areobtained in conversion operations.

Another object of the present invention is to provide an improvedprocess for the manufacture of nitration grade toluene in which thehydrocarbon constituents of the toluene may be readily separated as anitration grade product.

Accordingly, the improved process of the presas to a temperature from600 to 700 F. The resulting vapor products are then subjected to aseries of iractionating operations to' segregate out a distillateboiling within the range or from about 250 to 500 1''.

This distillate having the characteristics described hereinafter, isthereupon subjected to a particular type of conversion operation forconverting it into a product containing a substantial proportion oftoluene. by p ssing it in a conflned stream of restricted cross sectionthrough a heating zone in which it is vaporized and superheated to atemperature of from 800 to 1200 F.. and then digested in an enlargedreaction zone, either with or without contactwlth a catalyst. Theresulting products which will be comprised of toluene and high boilingconstituents boiling above that of toluene, as well as lower boilinghystock for the process is introduced into the apparatus at a pressureof from 200 to 500 lbs. per

6. The resulting highly heated products are conducted from the pipestill furnace through a transfer line l0 and introduced into the upperportion of a vertical reaction chamber l2, where the products arepermitted to react for a time sunlcient to convert the charging stockinto a final product containing a maximum of condensable constituentsboilingbelow about 500 F. The reaction products reaching the bottom ofthe chamber I2 are withdrawn through a line l4 and suddenly reduced intemperature by the introduction of a relatively cool fluid such as waterthrough a valved line l5. This cooling operation is preferablysuflicient to reduce the temperature of the cracked products to about700 F.. at which temperature they are introduced along with the coolingmedium into the lower portion of a vapor separating and scrubbingchamber l6 mounted below the reaction chamber l2. The high boilingconstituents are separated out in the bottom of the chamber it while thevapors are passed up around bafiles therein, and are scrubbed with aregulated proportion of high boiling distillate introduced into the uper part of the chamber 16 through a valved line H. Some of thedistillate introduced through the line I! is vaporized but theunvaporized portion together with the high boiling liquid constituentscollected in the bottom of the chamber l6 are withdrawn as fuel oilthrough a valved line ii. The vapor remaining uncondensed in the chamberl6, together with vaporized distillate, are discharged through a vaporline 20 at a temperature of from 600 to 700 F. and introduced into thelower portion of a fractionating tower 22.

The purpose of the fractionating tower 22 is to separat from the vaporconstituents the highboiling hydrocarbons distilling at temperaturesabove about 500 F. The resulting distillate is preferably used as arecycle stock in the process and therefore withdrawn through a line 24and forced by means of a pump therein into the line 2 to comprise avportion of the charging stock for th pipe still furnace 8. A portion ofthe stock in the line 24 may be conducted into the line H and used toscrub the vapors in i6. The vapors separated out in the tower 22 areconducted overhead through a vapor line 26, condensed in a condensertherein, and the resulting condensate and uncondensed constituentsconducted into a I 30 and forced by means of a pump therein (preferablycontrolled from a float in chamber 26), through a valved line 32 intothe tower 22, to control the fractionation therein, and through a valvedline 34 into a stabilizer tower 86.

The pressure maintained in the receiver 28 should be at least about 200lbs. per square inch,

. so that most of the C4 hydrocarbons will be condensed and notdischarged from the receiver with the gas. The pressures in the tower 22and chambers l2 and I! will be correspondingly higher, at leastsuflicient to cause the regular flow of vapors through the apparatus.

The condensable product recovered in the receiver 26 and conducted intothe stabilizer II through the valved line 24 will include hydrocarbonsboiling up to about 500 F. The cracking operation carried out in thepipe still furnace 8 and chamber I2 is preferably controlled, so thatthe gas oil charging stock, on a once through basis, is converted into acondensable product containing approximately 65% of constituents boilingbelow about 500 F., such constituents being largely unsaturated olefinicand aromatic hydrocarbons and substantially free of paraflinichydrocarbons having more than 5 carbon atoms.

The stabilizer 36 is preferabl operated at a pressur of about 300 lbs.per square inch, to produce a stable distillate at the bottom of thestabilizer which contains only the desired proportion of C4hydrocarbons, and which is substantially free of C: and lowerhydrocarbons. The overhead vapors from this stabilizer, comprisingsubstantially all of the lower hydrocarbons than C4, and the undesiredC4, are conducted through a vapor line 36, subjected to condensation ina condenser therein, and the resulting products passed into a receiver40, which may be used merely for the separation of suflicient condensateto be used as reflux for the control of the stabilizer 36. This refluxis passed from the receiver 40 through a line 42 and a pump therein intothe tower 36. Theexcess of light materials taken overhead from thstabilizer 36 is discharged from line 42 or through a pressure valvecontrolled vapor line from the receiver 40.

The stabilized'distillate produced in the stabilizer 36 is conductedthrough a valved line 44 and passed into a fractionating tower 46operated at a lower pressure than that maintained in the stabilizer 36.The stabilized distillate is fractionated in the tower 46 to takeoverhead a light gasoline fraction and leave a bottoms prodnot having aboiling range of from about 250- 500 F. The light gasoline is takenoverhead in vapor form, condensed and collected in a receiver, fromwhich a portion of the condensate may be returned to the upper part ofthe tower 46, while the light gasoline product is withdrawn to storagefor blending purposes.

The bottoms product withdrawn from the tower 46, and which should besubstantially free of parafllnic hydrocarbons is conducted through aline 48 and forced by mean of a pump therein at a pressure of about 500pounds per square inch through heating coils mounted in a pipe stillfurnace 60. The stock passed through this pipe still furnace ispreferably heated to a temperature sufllcient to vaporize the stock andsuperheat the vapors to a temperature of from 800 to 0 F., after whichthe vapor products are passed through a transfer line 62 into a catalystchamber 64 in which the vapors pass in intimate contact with a catalystadapted to convert the constituents of th vapors under cyclization andalkylation conditions into a product containing a maximum proportion oftoluene. Activated carbon is a suitable catalytic material and it may bedeposited on any suitable refractory material supported in chamber 64.Other catalysts such as the oxides of vanadium, chromium, manganese ,orcobalt, zinc chloride and other may be used. The catalytic action may beeil'ected in various other ways, as, for example, by suspending theactivated carbon or other catalyst in finely divided form in a stream orbody oi" high-temperature vapors as they are discharged from the furnace50 through the line 52. Activated carbon containing of a metal oxide orchloride is also suitable.

In most instances the high-temperature products passing through thechamber 5.4 are actually raised in temperature by the catalytic action,and care should be taken to prevent a temperature rise aboveapproximately 1060 F. The pressure in the chamber 54 should be fromabout 225 lbs. to about 350 lbs. per square inch.

The high temperature conversion products produced in the catalystchamber 54 are conducted therefrom into a line 56 and instantly chilledto a low temperature of approximately 600 F., by the introduction of arelatively cool fluid, preferably water, through a valved line 57. Theresulting relatively cool mixtur passes into a baffled separating andscrubbing chamber 58 in straw oil.

The absorber or'absorption tower 68 is operated under temperature andpressure conditions,

preferably a pressure of about 250 lbs. per quare inch, adapted toliberate all possible normally gaseou hydrocarbons of C3 and lower,while recovering the C4 and higher hydrocarbons. The unabsorbed gases inthe absorber 68 are discharged fromthe top of the absorber through apressure valve controlled line 89 as shown. The absorption medium usedin the tower 68 may be any suitable high boiling absorption oil, such asThe absorption medium is preferably separable from toluene bydistillation and is preferably used in sufllcient quantity to preventes.

cape of any toluene with the overhead gases. Back pressure is preferablymaintained from the tower 58 through apparatus elements 65, 62, 58, 54and 50. although considerable pressure drops through these elements maybe obtained by the which any high boiling materials are separated asliquid and withdrawn through a valved line 59 at the bottom of thechamber. The vapors separated out in the chamber 58, containing thedesired toluene and being substantially free of paraflinic hydrocarbonsare passed upwardly through the chamber in contact with a high boilingdistillate scrubbing oil introduced into the upper part of the chamberfrom a valved line 60. The oil introduced through the line 60 may behot,

or introduced in mall quantity. and not use to reduce the temperature ofthe vapor much below pha e. The condensate produced in the. tower iwithdrawn through a valved line 63 and forced by means of a pump thereininto. the line 48 leading to the pipe still furnace 50. A- portion ofthis distillate from the bottom of the towe 62 may be used in the top ofthe scrubber 58 by conducting a regulated portion thereof through theline 60. The distillate in the line 63 is hi hlv unsaturated and containa considerable oropor- 1 tion of aromatic hy r ca on a d is thereforevery suitable as stock for the furn ce 5" and the reactions carried outin the chamber 54.

The toluene and other constituents remaining in vapor form in thefractionatin tower 62 are conducted overhead through a vapor line 64.sub. iected to condensing conditions in a. condenser therein. and theresulting condensate anduncondensed gases conducted into a'recelver andwater separator 65. The water separat d out in the receiver is withdrawnthrou h a valved line from the bottom thereof. while the condensate anduncondensed gases are conducte through a line 66 into an absorber 68.- Aportion of the condensate separated out in the receiver is withdrawnthrough a valved line 61 and introduced into the upper part of thefractionating tower 62 to control the fractionation therein.

use of the. control valves provided. A higher pressure may be-used in 88than in 62 by pumping the materials in line 56 into the absorber 88.

The mixture of absorption medium and distillate collected in the base ofthe absorber 68. including the toluene and constituents boiling withinthe range of light gasoline as well as lower boiling normally gaseoushydrocarbons, is conducted through a line 10 and forced by means of apump therein into a stabilizer tower 12 in which the mixture isstabilized to eliminate overhead any propane and lower hy'drocarbonsaswell as excess C4 hydrocarbons not desirable in the light gasolinefraction from the standpoint of vapor pressure. The vapor fraction takenoverhead from the tower 12 is conducted through avapor line 14', and acondenser therein, and the mixed products are collected in a receiver 15from which the gases are discharged through a pressure valve controlledline while the Condensate is withdrawn through a valve controlled lineIS. A portion of this condensate is introduced into the top of thestabilizer 12 for controlling fractionation as indicated.

The stabilized mixture collected in the base of the tower I2 includingthe absorption medium. toluene and li ht gasoline. is conducted througha valved line 11 at substantially reduced pressure into a still 18 inwhich the toluene and light gasoline product is vaporized and separatedfrom the absorption medium which ma include all possible constituentsboiling above the boilin point of toluene under the conditions. Suchconstituents for example may include hydrocarbons boiling in thehigherboiling range portion of gasoline, in fact gasoline range materialboiling above toluene may be used as absorption-media. The vaporizedmaterials including the toluene are conducted from the still I8 througha vapor line 80 into a fractionating tower 82. while the absorptionmedium is withdrawn from the still 18 through a line 84 and forced bymeans of a pump therein through a cooler 86 mounted in the line. andthen into the upper portion of the absorption tower 58. Excess materialin lin 84 over that required in 68 may be used as gasoline blend-' ingstock or sent to the furnace 50.

The fractionation carried out in the tower 82 is preferably conducted insuch a manner that the light gasolineboiling range materials boilingbelow the boiling point of toluene are taken overhead while the tolueneis held back in the tower. The vapors from the tower 82 are conductedresulting product is collected in a receiver 90,

the overhead product introduced through a valve controlled line 94.

The toluene product produced in the operation and which may include someconstituents of substantially the same boiling point is withdrawn fromthe tower 82 through a valved line 96. The relatively pure toluenewithdrawn through the line 96 will be almost entirely free of paraflinichydrocarbons which normally cause considerable trouble in thefractionation of toluene made from coal. The product, however, maycontain small percentages of unsaturated oleflnic type hydrocarbonshaving about the same boiling point as toluene, and these may beeffectively removed by contacting the toluene product (in a well-knownmanner not shown) with sulfuric acid of from 64 to 66'B. gravitycontaining from 0.5 to approximately 1% of nitric acid. The product ispreferably refractionated after acid treatment, and such refractionationma be effected in the presence of a selective solvent or carrier agent.Toluene to be used for nitration purposes should be free of unsaturatedolefinic type hydrocarbons, have a boiling point of about 110 C., withan initial not below 108.5 C., and distilling completely at atemperature below 111 C, For certain purposes the toluene fractionremoved through the line 98 may be used directly,

preferably after acid treatment.

The charging stock for the pipe still furnace 50, as stated above,should be substantially free of parafllnic hydrocarbons. It preferablycomprises a mixture of unsaturated oleflnic and aromatic hydrocarbons ofwhich about20% are aromatics, although the proportion may run as high as35%. While this stock may possibly be secured from other sources than bythe method of production described above, no present source of suchmaterial is known. The charging stock for pipe still furnace 50therefore is preferably made in the manner described above. The lightgasoline in the tower 46 may be conveniently used for blending withstraight run gasoline or other suitable heavy gasoline stock, as forexample that from still 18.

From the foregoing description of the improved process of the presentinvention, it will be readily apparent that certain modifications may bemade therein without departing from the spirit and scope of theinvention as defined in the claim.

Having described the invention in its preferred form, what is claimed asnew is:

A process for the manufacture of toluene, which comprises passing ahydrocarbon charging stock in a confined stream of restrictedcross-section through a conversion zone and therein subjecting it tonon-catalytic cracking conditions at a temperature in the neighborhoodof 1000 F. for a sufilcient time to produce substantially a maximum ofcondensable constituents boiling below a temperature of about 500 F.which is substantially free of paraflin hydrocarbons having more thanfive carbon atoms to the molecule, quenching the resulting hightemperature conversion products and fractionating the same to recoverthe constituents boiling between about 250 and 500 F. as a separatefraction consisting essentially of oleflnes and aromatic hydrocarbons,passing this separate fraction through a separate heating and conversionzone maintained at a pressure of from 225 to 350 lbs. per square inchand subjecting the fraction to conversion condi tions at a temperaturein the neighborhood of v 1000 F. for a suihcient time to convert saidfrac-

